In sealing apparatuses for preventing the leakage of a sealed fluid, such apparatuses comprising two parts configured so as to rotate relatively to one another and so that end surfaces thereof slide along a plane, such as, for example, a mechanical seal, a balance must be struck between the two opposing conditions of seal tightness and lubrication in order to maintain seal integrity for extended periods of time. In recent years, environmental concerns in particular have led to an increase in demand for reduced friction in order to reduce mechanical damage while preventing sealed fluid leakage. Methods of reducing friction include the so-called fluid lubrication state, in which dynamic pressure is generated between sealing faces due to rotation, and the surfaces slide with a liquid film interposed therebetween. However, in such cases, positive pressure is generated between the sealing faces, so that the fluid escapes from the positive pressure portion outside of the sealing faces. Such fluid outflow constitutes leakage in the case of a seal.
Mechanical seals such as that shown in FIG. 10, in which dynamic pressure is generated between sealing faces via rotation, are known in the art (“first prior art”; see, for example, patent document 1). In the first prior art shown in FIG. 10, a plurality of radial direction grooves 32R, 32L for generating dynamic pressure during rotation is provided in the circumferential direction of a sealing face 31 of a mating ring 30 constituting one of a pair of sliding parts, with tapering surfaces 33R, 33L tapering in opposite directions being formed following the circumferential direction so that the boundary between one pair of radial direction grooves 32R, 32L is in a trough formed by the tapering surfaces, and a dam part 34 being formed at the boundary so as to separate the radial direction grooves 32R, 32L.
As shown in FIG. 10(b), when the sliding parts rotate relative to each another, the pressure in the radial direction groove 32R, which lies in the upstream direction of a gas flow G, decreases, creating negative buoyancy, and the wedge effect of the tapering surface 33L in the radial direction groove 32L on the downstream side of the dam part 34 increases pressure, creating positive buoyancy. At this time, the action of the dam part 34 decreases the negative pressure and increases the positive pressure, creating a net positive pressure and allowing a strong buoyancy to be obtained.
Meanwhile, the inventors have already filed a patent application for sliding members for a mechanical seal for sealing a sealed fluid present on one side in the radial direction of relatively rotationally sealing faces, wherein a plurality of grating portions 50, in which a plurality of parallel rectilinear indentations are formed at a predetermined pitch within a predetermined area, is discontinuously formed in a circumferential direction in an area between radii R2 and R3 on a sealing face 51 having an internal diameter R1 and an external diameter R4; the rectilinear indentations of the plurality of grating portions being formed so that the direction thereof inclines at a predetermined angle relative to the sliding direction of the sealing face, thereby improving the introduction and retention of the sealed fluid between the sealing faces, and allowing stable and favorable lubrication to be obtained, as shown in FIG. 11 (“second prior art;” cf. patent document 2).
In methods utilizing dynamic pressure to mitigate sliding resistance, as in the case of the first prior art, dynamic pressure is not generated until the shaft reaches a certain degree of rotational speed. For this reason, sufficient quantities of sealed fluid cannot be introduced between the sealing faces during the period from when rotation begins until dynamic pressure is generated, leading to a reduction in lubrication. When there is not a sufficient amount of sealed fluid between the sealing faces, torque increases, leading to the problems of seizing, vibration, noise, and the like being generated and sliding resistance becoming unstable.
The second prior art also has the problem that, because the height of the rectilinear indentations within the plurality of grating portions is on the order of 1 μm or less, a sliding member is deformed by heat, pressure, or load when operated for extended lengths of time in environments of high heat or pressure, partially increasing the size of the gap formed with the counterpart sliding member, so that the introduction and retention of the sealed fluid between the sealing faces cannot be controlled by fine indentations of roughly 1 μm in height.